PHOTOSYSTEM-II CORE PHOSPHORYLATION HETEROGENEITY, DIFFERENTIAL HERBICIDE BINDING, AND REGULATION OF ELECTRON-TRANSFER IN PHOTOSYSTEM-II PREPARATIONS FROM SPINACH

The effect of photosystem II core phosphorylation on the secondary quinone acceptor of photosystem II (Q(B)) domain environment was analyzed by comparative herbicide-binding studies with photosystem II preparations from spinach (Spinacia oleracea L.). It was found that phosphorylation reduces the binding affinity for most photosynthetic herbicides. The binding of synthetic quinones and of the electron acceptor 2,6-dichlorophenolindophenol is also reduced by photosystem II phosphorylation. Four photosystem II core populations isolated from membranes showed different extents of phosphorylation as well as different degrees of affinity for photosynthetic herbicides. These findings support the idea that heterogeneity of photosystem II observed in vivo could be, in part, due to phosphorylation.